Connected: An Internet Encyclopedia
RFC 1583 - 12. Link State Advertisements

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### 12. Link State Advertisements

Each router in the Autonomous System originates one or more link state advertisements. There are five distinct types of link state advertisements, which are described in Section 4.3. The collection of link state advertisements forms the link state or topological database. Each separate type of advertisement has a separate function. Router links and network links advertisements describe how an area's routers and networks are interconnected. Summary link advertisements provide a way of condensing an area's routing information. AS external advertisements provide a way of transparently advertising externally-derived routing information throughout the Autonomous System.

        Type   Dest        Area   Path  Type   Cost   Next     Adv.
                                                      Hop(s)   Router(s)
        ________________________________________________________________
        N      Ib          0      intra-area   16     RT3      *
        N      Ia          0      intra-area   21     RT3      *
        BR     RT3         0      intra-area   1      *        *
        BR     RT10        0      intra-area   16     RT3      *
        BR     RT11        0      intra-area   19     RT3      *
        ________________________________________________________________
        N      N9-N11,H1   0      inter-area   20     RT3      RT11

                      Table 14: Changes resulting from an
                            additional virtual link.

Each link state advertisement begins with a standard 20-byte header. This link state advertisement header is discussed below.

12.1. The Link State Advertisement Header

12.1.1. LS age
12.1.2. Options
12.1.3. LS type
12.1.4. Link State ID
12.1.5. Advertising Router
12.1.6. LS sequence number
12.1.7. LS checksum

12.2. The link state database
12.3. Representation of TOS
12.4. Originating link state advertisements

12.4.1. Router links
12.4.2. Network links
12.4.3. Summary links
12.4.4. Originating summary links into stub areas
12.4.5. AS external links

Next: 12.1. The Link State Advertisement Header

Connected: An Internet Encyclopedia
RFC 1583 - 12. Link State Advertisements